Recent progress in shape memory polymer: New behavior, enabling materials, and mechanistic understanding

Abstract

Shape memory polymers (SMPs), as a class of programmable stimuliresponsive shape changing polymers, are attracting increasing attention from the standpoint of both fundamental research and technological innovations. Following a brief introduction of the conventional shape memory effect (SME), progress in new shape memory enabling mechanisms and triggering methods, variations of in shape memory forms (shape memory surfaces, hydrogels, and microparticles), new shape memory behavior (multi-SME and two-way-SME), and novel fabrication methods are reviewed. Progress in thermomechanical modeling of SMPs is also presented. Abbreviations:SCPs shape changing polymers; LCEs liquid crystalline elastomers; SMP shape memory polymer; SME shape memory effect; 2W two-way; 1W oneway; T trans transition temperature; T g glass transition temperature; T m melting temperature; T cl liquid crystal cleaning temperature; T d deformation temperature; T f shape fixing temperature; T c crystallization temperature; R f shape stability ratio; R r shape recovery ratio; T sw switching temperature; ε max maximum recoverable strain; σ max maximum recovery stress; SMC shape memory cycle; ε load strain under load; ε fixed strain; T r recovery Page 2 of 106 A c c e p t e d M a n u s c r i p t 2 temperature; ε rec recovered strain; V r strain recovery rate; T σmax temperature corresponding to σ max ; T sw,app apparent switching temperature; PCL poly(ε-caprolactone); SMPU shape memory polyurethane; EMU elemental memory unit; TME temperature memory effect; PU polyurethane; T i liquid-crystal isotropic transition temperature; T v vitrification temperature; CIE crystallization induced elongation; MIC melting induced contraction

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

“…Synthetic SMPs have been demonstrated that show multiple shapes, cycling between three or more intermediary stages with varying stimulus intensity (multi-way SMP), and that can reversibly cross between two programmed states, rather than just returning to the lowest energy state (2 W-SME) [70].…”

“…Hydrogels may change volume by as much as 1100 times [99] in response to chemical, hygroscopic, heat, or light triggers, and may also exhibit shape memory characteristics [70,100]. Properties depend on crosslink density, choice of polymer, copolymer or blend, nature of cross-link bonding [101], and solvent.…”

Effects of Loading Rate on the Relaxation and Recovery Ability of an Epoxy-Based Shape Memory Polymer

“…The mechanisms that drive SMPs have been covered in great detail in the open literature [2,[28][29][30][31]. A brief recap of these mechanisms is warranted here for completeness.…”

Thermal Sensitive Shape Memory Behavior of Epoxy Composites Reinforced with Silicon Carbide Whiskers

“…Shape memory polymers (SMPs) are stimuli-responsive materials that can assume a temporary shape and recover their original shape when triggered through an external stimulation such as thermal stimulus, electric current, light, magnetic field, moisture, and pH value [1][2][3][4][5][6][7][8]. Thermally induced SMPs are the most common type of SMP.…”